Determination of moisture by electrolysis



P 1964 L. M. JOHNSON ETAL 1 3,147,202

DETERMINATION OF MOISTURE BY ELECTROLYSIS Filed March 18, 1960 "METER COOLING BATH GAS OUT GAS lN GASOUT GASIN r; 3 1 J,

COATED ELECTRODES TUBE ,OOOLING 22 COIL ELECTROLYTIC CELL l6 CELL v HOLDER as I 1 INVENTORS. LEE M. JOHNSON, LELAND w. POHLER,

3,147,202 DETERMINATIUN F MOISTURE BY ELECTRQLYSIS Lee M. Johnson and Leland W. Pohler, Baytown, Tex.,

assignors, by mesne assignments, to Esso Research and Engineering Company, Elizabeth, N..I., a corporation of Delaware Filed Mar. 18, 1960, Ser. No. 16,036 Claims. ((31. 204-4) The present invention is directed to a method for determination of moisture in a fluid such as a gas or a gasiform material. More particularly, the invention is concerned with a method for determination of moisture in which a coulometric method is employed. In its more specific aspects, the invention is concerned with the determination of moisture in fluids containing oxygen and hydrogen and in which the moisture is present in parts per million.

The present invention may be briefly described as a method for determination of moisture in a fluid containing a reactive gas such as oxygen and hydrogen in which the fluid is passed into contact with a hydroscopic substance which is electrically conductive only when Wet which, in turn, is in contact with electrodes across which a DC. potential is imposed and moisture is decomposed to hydrogen and oxygen and in which a signal is displayed indicating the amount of moisture. The particular feature of the present invention is adjusting the temperature of the gasiform fluid, the electrodes, and the hydroscopic substance to a temperature below that at which substantial recombination of hydrogen and oxygen occurs in significant amounts in the determination of moisture in said environment.

In the practice of the present invention, the water determination is electrolytic and may be conducted in apparatus such as described in the Keidel Patent 2,830,945, issued April 15, 1958. While water may be determined electrolytically, such determination is attendant with difficulties when hydrogen or oxygen is present because of inaccurate results which have been obtained. The inaccurate results have led to the necessity of applying a correction factor in the electrolytic determination of moisture in fluid such as gas and gasiform material which contain hydrogen or oxygen. It has now been discovered in determination of moisture electrolytically in a fluid containing hydrogen or oxygen that the inaccurate results are obtained because of recombination of hydrogen and oxygen in the presence of the electrodes employed in the electrolytic determination of moisture. In accordance with this invention, it is now possible to determine moisture in hydrogenand oxygen-containing fluids with extreme accuracy. By virtue of adjusting the temperature of the fluid, the electrodes, and the hydroscopic substance to a temperature below that at which substantial recombination of hydrogen occurs in significant amounts, it is possible to obtain a correct determination of the moisture content of the fluid.

The present invention will be further illustrated by reference to the drawing in which:

FIG. 1 is a schematic view of an apparatus by way of which the present invention may be conducted;

FIG. 2 is a sectional view of the electrolytic cell of FIG. 1; and

ice

FIG. 3 illustrates a preferred embodiment of apparatus for conducting the method of the present invention.

Referring now to the drawing and particularly to FIG. 1, numeral 11 designates a charge line by way of which a hydrogenor oxygen-containing stream containing moisture is led into a coil 12 arranged in a cooling bath 13 which may contain cool fluid 14 such as water or any other cooling fluid maintained at a temperature below that at which recombination of hydrogen and oxygen would occur in the apparatus employed in the present invention. Coil 12 connects by line 15 into an electrolytic cell 16, which may be of the type as described in the Keidel patent supra. In electrolytic cell 16, the moisture in the feed gas introduced by line 11 is decomposed to oxygen and hydrogen and a signal is transmitted by electrical signal leads 17 and 18 to a meter 19 in which the moisture content is indicated in parts per million on scale 20 in indicator 21.

In accordance with the present invention, the feed gas, the electrodes, and hydroscopic substance in cell 16 are cooled to a temperature below that at which hydrogen and oxygen recombine in cell 16. This temperature is below about 50 F. and preferably is in the range from about 0 to about 50 F. Therefore, the temperature of the feed gas must be reduced from a temperature in the range from about 60 F. to about 150 F. to below 50 F. to obtain the improved results.

The feed gas may be substantially pure hydrogen or substantially pure oxygen containing small amounts of water ranging up to about parts per million or more. Ordinarily the feed gas will contain less than 500 parts per million of moisture and smaller amounts. By cooling the feed gas, the electrodes and the hydroscopic substance in accordance with the present invention, the water content of the feed gas is determined accurately and displayed on meter 19. The feed gas contains at least about 50% of oxygen or hydrogen.

Referring now to FIG. 2, a sectional view of the cell 16 is shown. Cell 16 is comprised essentially of a tube 22 which is provided with an inlet 23 which connects to line 15 and an outlet 24 which connects to line 25 of FIG. 1. Arranged in the tube 22 are platinum electrodes 26 and 27, which are suitably connected to a power source of direct current. Energyis supplied to electrodes 26 and 27 by way of leads 28 and 29. The gas is introduced by inlet 23 and is removed by outlet 24 connecting to line 25. As the gas flows through tube 22, power is supplied through leads 28 and 29, which connect to leads 17 and 18, connecting in series with the meter 19. As shown in FIG. 1, the power supply 30 (DC) shown in lead 18 causes electrolysis of the moisture when absorbed by the hydroscopic substance which coats the electrodes 26 and 27. As a result thereof, a signal is transmitted to meter 19 and the signal which is indicative of the water content is displayed on a scale 20.

In FIG. 2, the hydroscopic substance is phosphorus pentoxide but other hydroscopic substances such as potassium carbonate, potassium hydroxide, sodium carbonate, sodium hydroxide, and barium hydroxide may be employed. As shown in FIG. 2, the tube 22 may be embedded in a plastic material 31 for protection of the tube 22.

Referring now to FIG. 3, an electrolytic cell such as 16 having a line 15 conducting gas thereto and line 25 conducting gas therefrom is provided. In this particular instance, the line 15 is cooled by circulating a cooling fluid through a cool coil 32 which is employed to trace line 15 and which is extended around a cell holder 35 containing the cell 16. The cell holder 35 and the coil 32 may be suitably insulated by insulation means 33 which surrounds the cell holder 35, the line 15, and the coil 32. The cooling solution is discharged from the coil 32 by line 34'.

In order to illustrate the invention further, a number of runs were made on a hydrogen-containing gas employing apparatus such as illustrated in the drawing. In these operations, the electrolytic cell temperature was varied from above 100 F. to below 50 F. The results obtained are shown in the following table.

Table I H2O in H Cell No. Cell Temperature H2O in Instrument H; (p.p.m.) Reading (an- A About 85 F 1 18 A Above 100 F 1 50 1 6 1 1 181 180 It will be noted from the data shown in Table I that when the temperature of the cell and the gas was above 50 F., the instrument reading in p.p.m. varied SO-fold greater than the actual water content whereas when the temperature was below 50 F., accurate results were obtained.

Other runs were made at cell and gas temperatures of 23 F., 41 F., 2 F., 40 F., and 5 F. on hydrogen streams which contained varying amounts of water. These results are shown in the following Table II.

Table II Cell Temperature H2O in H; Inst. Reading F.) (p.p.m.) H2O in H2 (ppm) It will be seen that the instrument reading when the temperature was below 50 F. correspond closely with the actual water content of the hydrogen stream.

In order to illustrate further the practice of the present invention, determinations were made of water in oxygencontaining streams with a cell and gas temperature of 40 F. These results are shown in Table HI.

Examination of the data in Table III shows that accurate results are obtained in analyzing moisture-containing oxygen streams. A number of runs were made at temperatures above 50 F. In these operations at elevated temperatures, inaccurate results were obtained.

In the several operations employed to exemplify the invention, phosphorous pentoxide was employed as the hydroscopic substance.

It will be seen from the number of runs made that extremely accurate determinations of moisture in hydrogenand oxygen-containing streams may be effected.

The present invention is quite advantageous and useful in that it is now possible to determine accurately the amount of moisture in hydrogenand oxygen-containing streams. Such streams are encountered in the steel industry and in the petroleum industry. Particularly in the petroleum industry, it is frequently necessary to control carefully the amount of moisture in hydrogen streams which are employed in catalytic conversion of hydrocarbons such as in hydroforming and hydrofining operations. Also, in the steel industry where reduction operations are conducted, it is extremely important to determine the moisture content of hydrogen-containing streams.

As will be seen from the foregoing description and the numerous examples, the present invention is based on a discovery that the electrolytic determination of moisture may be made extremely accurate if conducted at tempcratures below about 50 F.

The nature and objects of the present invention having been completely described and illustrated, what we wish to claim as new and useful and secure by Letters Patent 1s:

1. In the determination of moisture in a gasiform fluid passed into contact with a hydroscopic substance which is electrically conductive only when wet, which substance is in contact with electrodes across which direct current is imposed and moisture is decomposed to hydrogen and oxygen, said fluid containing a substantial amount at least about 50% of a reactive gas selected from the group consisting of oxygen and hydrogen, the improvement which comprises establishing and maintaining the temperature of said fluid, said electrodes and said substance during said determination of moisture at a value below about 50 F. at which substantial recombination of hydrogen and oxygen in significant amounts is suppressed therein.

2. A method in accordance with claim 1 in which the reactive gas is oxygen.

3. A method in accordance with claim 1 in which the reactive gas is hydrogen.

4. In the determination of moistuure in a gasiform fluid at a temperatuure substantially above 50 F. which is to be passed into contact with a hydroscopic substance which is electrically conductive only when wet, which substance is in contact with electrodes across which direct current is imposed and moisture is decomposed to hydrogen and oxygen, said fluid containing at least 50% of a reactive gas selected from the group consisting of oxygen and hydrogen, the improvement which comprises lower- 5 ing the temperature of said fluid, said electrodes and said substance to a temperature below about 50 F. at which substantial recombination or" hydrogen and oxygen in significant amounts is suppressed therein and carrying out the electrolytic determination of the moisture content of said fluid while maintaining said lowered temperature.

5. In the electrolytic determination of the water content of a gasiform fluid containing as a major portion one of the atomic constituents of water, wherein the contained water is electrolytically decomposed into hydrogen and oxygen the improvement which comprises establishing and maintaining the electrolytic reaction at a temperature less than 50 F. at which substantial recombination of 6; hydrogen and oxygen in significant amounts is suppressed therein.

References Cited in the file of this patent UNITED STATES PATENTS 2,830,945 Keidel Apr. 15, 1958 

1. IN THE DETERMINATION OF MOISTURE IN A GASIFORM FLUID PASSED INTO CONTACT WITH A HYDROSCOPIC SUBSTANCE WHICH IS ELECTRICALLY CONDUCTIVE ONLY WHEN WET, WHICH SUBSTANCE IS IN CONTACT WITH ELECTRODES ACROSS WHICH DIRECT CURRENT IS IMPOSED AND MOISTUE IS DECOMPOSED TO HYDROGEN AND OXYGEN, SAID FLUID CONTAINING A SUBSTANTIAL AMOUNT AT LEAST ABOUT 50% OF A REACTIVE GAS SELECTED FROM THE GROUP CONSISTING OF OXYGEN AND HYDROGEN, THE IMPROVEMENT WHICH COMPRISES ESTABLISHING AND MAINTAINING THE TEMPERATURE OF SAID FLUID, SAID ELECTRODES AND SAID SUBSTANCE DURING SAID DETERMINATION OF MOISTURE AT A VALUE BELOW ABOUT 50*F. AT WHICH SUBSTANTIAL RECOMBINATION OF HYDROGEN AND OXYGEN IN SIGNIFICANT AMOUNTS IS SUPPRESSED THEREIN. 